The purpose of the proposed research is to investigate the relationship between insulin and hepatic macrophages (i.e., Kupffer cells) with respect to their insulin-degradation capacity and the influence of both insulin and glycemia on phagocytosis by these cells. Liver cells are to be isolated into pure populations of hepatocytes and Kupffer cells by enzymatic digestion of perfused rat livers and subsequent magnetic separation of macrophages pre-loaded with iron according to the method of Wincek et al. The two hepatic degradative enzymes, glutathione-insulin transhydrogenase and insulin-specific protease, are to be purified and quantified according to the standard procedures of Ansorge et al and Burghen et al, respectively, in the two cell populations. The uptake of insulin by the two cell populations in vitro will also be compared. The influence of streptozotocin-induced diabetes mellitus as well as subsequent insulin replacement theory on phagocytosis by the reticuloendothelial system will be evaluated both in rats in vivo and in perfused rat livers. RES phagocytic function is to be quantified by determining the clearance half-time for carbon particles following intravenous administration. In addition, the influence of insulin (single dose and continuous administration) as well as perfusate glycemia on Kupffer cell phagocytosis, insulin clearance, and glucose uptake by perfused rat livers will be investigated. Rat livers are to be perfused with twenty percent heparinized whole rat blood with Krebs-Ringer bicarbonate buffer under conditions of constant temperature (37 degrees C), flow (25 ml/min), and gas supply (95% O2 - 5% CO2). The longterm objectives are to determine if RES phagocytic dysfunction contributes to the higher incidence of infections in patients with uncontrolled diabetes mellitus and why higher insulin doses are required for diabetics with infections.